1- The Yerebatan Cistern built by Emperor Justinian in 532 is also known as the Basilica Cistern because it is located under the Stoa Basilica. The cistern is a giant structure covering a rectangular area of 140 meters in length and 70 meters in width. There are 336 columns, each 9 meters high, inside the cistern, which can be accessed by a 52-step stone staircase. These columns, erected 4.80 meters apart from each other, form 28 rows of 12 rows in each row.
2- These columns, rising in the water, remind of an endless forest and impress the visitor as soon as they enter the cistern. The weight of the ceiling of the cistern was transferred to the columns by means of arches, with the cross-shaped vaults rounded. Most of the columns, which are understood to have been collected from older structures and were carved from granite of various marble types, consist of one piece, and some of them consist of two pieces on top of each other. The headings of these columns have different characteristics in places. 98 of these reflect the Corinth style, while some of them reflect the Doric style. The walls of the cistern built of brick, 4.80 meters thick, and the brick-paved floor were plastered with a thick layer of Khorasan mortar, making it waterproof. This cistern, which has a total area of 9,800 square meters, has a water storage capacity of approximately 100,000 tons.
3- The water of the cistern, where 7,000 slaves worked in its construction, was 19 km from the city with the help of the 971-meter-long Valens (Bozdoğan) arch built by the emperor Valens (368) and the 115.45-meter Maglova Arch built by the emperor Justinianus. It was brought from the center of Eğrikapı water division in Belgrat forests. Most of the columns in the cistern are cylindrical, except for a few that are angular or grooved. Among these columns, the one which is decorated with the repetition of the Peacock Eye, Pendent Branch and Tear in engraving and embossing is especially noteworthy. This column, called “Farum Tauri” in the Byzantine period, and the ruins of which was found in Beyazid square is similar to the columns in the triumphal arch of the great Theodesius (379-395) of the time.
4- The two Medusa heads used as pedestals under the two columns in the northwest corner of the cistern are the masterpieces of Roman Age sculpture. The cistern watched in amazement by those who came to visit. Although there is no definite information as to which building these heads were taken from, it is thought that they were brought here from an ancient structure belonging to the Young Roman Age.
5- The Basilica Cistern was used for a while after the conquest of Istanbul by the Ottomans in 1453, and water was given to the gardens of Topkapi Palace, where the sultans lived. The cistern, which seemed to have not been used by the Ottomans, who preferred tap water, that is, flowing water, instead of stagnant water after establishing their own water facilities in the city, was rediscovered by Dutch traveler P. Gyllius, who came to Istanbul in 1544-1550 to research the Byzantine remains.
6- Basilika Cistern has undergone various repairs since its establishment. The first restoration of the cistern, which was restored twice during the Ottoman Empire period, was by Architect Kayserili Mehmet Ağa during the time of III. Ahmet in the 18th century. The second major repair was in during the time of Sultan II. Abdülhamit (1876-1909). The biggest repair in the Republic period was made in 1985. With the removal of 50.000 tons of mud and the construction of the excursion platform, it was completed on September 9, 1987 and opened to visitors again.